This invention is directed to drills and more particularly to control systems that permit forward or reverse rotation of the operating head of the drill. The invention is particularly directed to a control system that permits automatic alternate forward and reverse rotation of the operating head upon successive actuations of the drill.
Drills with operating heads that can be rotated in reverse directions are well known. Such drills usually include a trigger or other manually operable member that actuates the drill motor and/or controls the motor speed in a particular selected direction.
The direction in which the operating head or motor moves is normally established by the setting of another manually operable member such as a switch, button or lever provided on the drill such as shown, for example, in U.S. Pat. No. 4,095,072 for a drill with a direction reversing switch. A disadvantage of this drill is that it requires two-handed operation when a change of direction is needed.
U.S. Pat. No. 4,459,522 shows a drill with two separate switches for operating the motor in opposite directions. A common rocker actuates either of the two switches individually or jointly. A disadvantage of this drill is the likelihood of inadvertent or unintentional actuation of the drill motor in a nonpreferred direction because both directions are controlled by a common rocker.
U.S. Pat. No. 3,171,292 discloses an electric actuator which causes forward rotation upon depression of a trigger and reverse rotation upon release of a trigger. However, reverse rotation is obtainable only when there is a restraint against forward rotation. A disadvantage of this drill is that it must go through a forward cycle before a reverse cycle can be obtained.
It is well known that tapping operations performed with a drill often require repeated switching of the drill from a forward operating mode to a reverse operating mode and back again. Thus the drill is used to power tap for a desired number of revolutions and is then operated in reverse to break the chips that are cut by the tap.
In a surgical tapping operation, during tapping of a bone, forward and reverse sequencing are used repeatedly. The need to perform a different actuation for each rotational mode such as forward and reverse, can lead to mistakes whereby a drill is caused to rotate in a nonpreferred direction.
Furthermore, it is often necessary to remove the drill from the object being tapped in order to accomplish the necessary directional change. Removal of the drill can be an inconvenience and hampers the performance of the tapping operation.
It is thus desirable to provide a drill which will automatically operate in alternating forward and reverse directions upon successive actuations of the drill.